1. Field of the Invention
The present invention pertains to a method and apparatus for performing cementing operations in oil or gas wells. More particularly, the present invention pertains to a method and apparatus for performing cementing operations in oil or gas wells using a remotely-operated rotating cement head having a high tensile strength.
2. Brief Description of the Prior Art
Exploration and development of offshore oil and gas reserves can be extremely risky and expensive undertakings. When a fixed platform or other structure is already in place, wells can typically be drilled using a platform-supported drilling rig. However, because of the high cost required to design, fabricate and install fixed structures and associated production facilities and equipment, this investment is often deferred until after the existence of sufficient oil and gas reserves has been proven through exploratory drilling operations. As a result, many offshore wells, particularly exploratory wells and/or wells drilled in deep water environments, are drilled using floating drilling rigs such as drill ships and semi-submersible drilling rigs prior to installation of a permanent platform or other similar structure.
Drilling operations conducted from floating drilling rigs differ from those conducted from permanent structures in many important respects. One important difference is the location of blowout preventer and wellhead assemblies. When drilling from a fixed platform or other similar structure, a blowout preventer assembly is typically located on the platform or other structure. However, when drilling from a floating drilling rig, blowout preventer and wellhead assemblies are not located on the drilling rig, but rather on the sea floor. As a result, specialized equipment known as “subsea” or “subsurface” blowout preventer and wellhead assemblies must be utilized.
Cementing operations are frequently made more complicated by the use of such subsea equipment. In subsea well drilling applications, a cement head is typically installed above the rig floor to provide a connection or interface between a rig's pipe lifting system and surface pumping equipment, on the one hand, and down hole work string or other tubulars extending into a well, on the other hand. Such cement heads must permit cement slurry to flow from a pumping assembly into the well, and should have sufficient flow capacity to permit high pressure pumping of large volumes of cement and other fluids at high flow rates. Such cement heads must also have sufficient tensile strength to support heavy weight tubulars extending from the surface into a well, and to accommodate raising and lowering of such tubular goods. Cement heads should also beneficially swivel in order to permit rotation of the tubular goods and/or other downhole equipment in a well while maintaining circulation from the surface pumping equipment into the down hole tubular goods extending into the well.
Darts, balls, plugs and/or other objects, typically constructed of rubber, plastic or other material, are frequently pumped into a well in connection with conventional cementing operations. In many instances, such items are suspended within a cementing head until the objects are released or “launched” at desired points during the cement pumping process. Once released, such items join the cement slurry flow and can be pumped down hole directly into a well. Such darts, balls, plugs and/or other objects should be beneficially held in place within the slurry flow passing through the cement head prior to being launched or released without being damaged or washed away by such slurry flow.
In many cases, cement heads must be positioned high above the rig floor during cementing operations. In such instances, a cement head will typically be located out of reach of personnel working on the rig floor, making it difficult for such personnel to easily access the cement head in order to actuate valves and/or launch items into the well. Frequently, personnel must be hoisted off the rig floor using a makeshift seat or harness attached to a winch or other lifting device in order to reach the cement head to actuate valves and/or launch darts, balls, plugs or other objects. Such personnel are at risk of falling and suffering serious injury or death. Moreover, such personnel are frequently required to carry heavy bars, wrenches and/or other tools used to manipulate valves or other equipment on such cement heads. These bars, wrenches and/or other heavy tools are at risk of being accidentally dropped on people or equipment on the rig floor below.
Thus, there is a need for a lifting top drive cement head that permits cement flow into the cement head from above, and has a high tensile strength as well as the ability to rotate or swivel. Valves used to isolate or restrict flow through the cement head, as well as launching mechanisms for releasing darts, balls, plugs and/or other objects into the slurry flow, can be remotely actuated from a safe distance to eliminate the need for lifting personnel off the rig floor. Audible and/or visual indicators should also be provided to alert personnel on or in the vicinity of the rig floor about the operation of various elements of the tool and/or the status of objects launched into a well.